1. Explain the following: Spontaneous emission, Stimulated emission, Meta-stable state, Population inversion, Pumping and Resonant Cavity. 2. With a neat labelled diagram, explain... 1. Explain the following: Spontaneous emission, Stimulated emission, Meta-stable state, Population inversion, Pumping and Resonant Cavity. 2. With a neat labelled diagram, explain the construction and working of He Ne laser. 3. Derive an expression of Numerical Aperture for step index fiber and also state the significance of it. 4. Draw profile index and path ray diagrams for step index and graded index fiber. Differentiate Step index fiber and Graded index fiber. 5. Explain the working of the optical fiber communication system with a block diagram. What are the merits of optical fibre communication system? 6. A light ray enters an optical fiber of core refractive index 1.49 and cladding refractive index 1.475. Find the following: Critical Angle at core-cladding interface, V Number, and Number of modes travelling through fiber of core radius 10 µm and 1150 nm is wavelength of light. 7. If light enters fiber through water medium of refractive index 1.33, find acceptance angle for the optical fiber of core and clad refractive indices 1.51 and 1.49 respectively. Also find number of modes that fiber supports. (Given: operating wavelength is 850 nm and core radius is 15 µm.) 8. Calculate de Broglie wavelength and velocity associated with an α-particle accelerated by a potential difference of 100 kV. Mass of α-particle is 6.68 × 10^-27kg. State and explain de Broglie Hypothesis. 9. State de Broglie hypothesis. An electrically charged particle with charge 4.5 µC and mass 1.53 × 10^-27kg is accelerated from rest through a potential difference of 200 V. Calculate the associated wavelength and kinetic energy of electron beam in eV. 10. State and explain the Uncertainty principle. The speed of an electron is measured to within an uncertainty of 1100 m/s. What is the minimum space required by the electron to be confined to an atom? Read more

1. Spontaneous emission, stimulated emission, meta-stable state, population inversion, pumping, resonant cavity: fundamental laser concepts. 2. He-Ne laser: helium transfers energy to neon, causing coherent light emission. 3. NA = √(n1²-n2²); significance: light-gathering capacity. 4. Step vs graded index: profile/form affects dispersion. 5. Optical fiber system: high bandwidth, low signal loss. 6. θc ≈ 84.7°, V ≈ 12.03, modes ≈ 72. 7. θa ≈ 8.3°, modes ≈ V²/2. 8. λ ≈ 9.59x10⁻¹⁵ m for 100 kV α-particle. 9. de Broglie: wave-particle duality; 200 eV KE. 10. Δx ≥ 5.79 x 10⁻¹⁰ m.

1. Spontaneous Emission is the process where an excited electron falls to a lower energy level, emitting a photon without external influence. Stimulated Emission, key to laser operation, is when an incoming photon causes an excited electron to emit a photon of the same energy. Meta-stable State is a long-lived excited state, crucial for laser action. Population Inversion occurs when more electrons are in excited states than ground states. Pumping is the process of supplying energy to achieve population inversion. Resonant Cavity confines light to amplify it.
2. He-Ne Laser: The construction includes a gas discharge tube with helium and neon, a pair of mirrors, and an optical cavity. The working involves helium atoms transferring energy to neon atoms, causing stimulated emission of coherent light.
3. Numerical Aperture (NA) for step-index fiber is derived as NA = √(n1² - n2²), where n1 and n2 are core and cladding indices. It indicates the light-gathering ability.
4. Step Index Fiber: The index profile is a sharp step. Graded Index Fiber: The index gradually changes, reducing dispersion. Step-index offers distinct light paths, while graded-index provides smoother paths, reducing signal distortion.
5. Optical Fiber Communication System: Converts electrical signals to optical, transmits via fiber, and reconverts. Merits include high bandwidth, low loss, and immunity to electromagnetic interference.
6. Critical Angle: θc = sin⁻¹(n2/n1). V-number (V) = (2πa/λ)√(n1² - n2²). Modes ≈ V²/2. With n1 = 1.49, n2 = 1.475, a = 10µm, λ = 1150nm: θc ≈ 84.7°, V ≈ 12.03, Approx. modes ≈ 72.
7. Acceptance angle (θa) = sin⁻¹(√(n1² - n2²)), using water’s n medium: θa = sin⁻¹(√(n1² - n²)/n_medium). With n1 = 1.51, n2 = 1.49, n_medium = 1.33, a = 15µm, λ = 850nm: θa ≈ 8.3°, modes ≈ V²/2.
8. de Broglie Wavelength: λ = h/p = h/√(2meV), for α-particle, V = 100 kV, m = 6.68×10⁻²⁷kg, λ ≈ 9.59x10⁻¹⁵ m.
9. de Broglie Hypothesis: All matter exhibits wave-particle duality. For charge Q = 4.5 µC, m = 1.53×10⁻²⁷kg, V = 200 V, λ = h/√(2meQV), KE = 200 eV.
10. Uncertainty Principle: ΔxΔp ≥ ħ/2. For electron, Δv = 1100 m/s, minimum Δx ≈ 5.79 x 10⁻¹⁰ m.